1. Field of the Invention
The present invention relates to a piston type gas compressor to be used for the supply, in an oil-free condition, such a gas as argon or nitrogen used in a hot isostatic pressing (HIP) apparatus or the like, which compressor uses a gas of several ten to 200 kgf/cm.sup.2 as a gas source and generates a high-pressure gas of several hundred kgf/cm.sup.2 or higher.
More particularly, the present invention is concerned with a piston type gas compressor wherein a seal ring used in a piston portion, which seal ring is of a high replacement frequency, can be replaced with a new one without removal of pipes, etc.
2. Description of the Prior Art
Reference is here made to Japanese Patent Publication No. 57233/90. In this patent publication there is disclosed "a compressor comprising a cylinder having a flange at one end thereof and a packing at the opposite end thereof, a cylinder head connected removably to the said flange, a piston rod extending at one end thereof into the cylinder through the packing, means for reciprocating the piston rod toward and away from the cylinder head, a free piston disposed within the cylinder and adapted to be engaged by the rod, a port for a pressure fluid which port is formed in the cylinder head, and means for introducing the fluid at a positive pressure into the cylinder through the port when the piston rod is spaced away from the cylinder head and for discharging the fluid as a high-pressure fluid from the cylinder through the port when the piston retreats toward the cylinder head." According to this prior art compressor: "By unscrewing the cylinder head, the piston can be removed easily, thus permitting replacement of the packing of the piston. When the packing of the piston is worn out to such a degree as requires replacement, it is not necessary to touch the tie rod which holds the components of the compressor in an assembled relation. All that is required is to remove common lines (pipes) from the cylinder head and remove the cylinder head."
Recently, studies have been made to utilize hot isostatic pressing in the manufacture of a very large scale integrated circuit, such as silicon wafer. It is to be noted that in the field of very large scale integrated circuits it has become necessary to take measures to cope with environments or conditions different from those so far applied to high-pressure equipment such as HIP apparatus.
Firstly, it is important to diminish particles up to the limit which particles are mixed into a processing gas in the interior of the apparatus halfway of the process. Particularly, the incorporation of transition metal particles causes a serious problem in the manufacture of a very large scale integrated circuit such as silicon wafer. In this connection, a compressor of such a structure as generates metallic worn particles poses a problem, and no consideration is given to a countermeasure in the foregoing conventional compressor.
Although the basic motion of the piston is a sliding motion, it is the portion of a piston packing that is in contact with the inner surface of the cylinder, so it is very likely that the piston will tilt from the axis of the cylinder. If the packing undergoes a local wear or tilts, the metallic portion of the piston comes into contact with the cylinder and generates metallic particles, which is not desirable.
Moreover, in process gas pipe lines in such an apparatus for the manufacture of a very large scale integrated circuit, particles are apt to be generated at pipe joint portions or valve portions. Particularly, there is a strong tendency to avoid such a structure as requires removal of pipe joint portions in maintenance, and a welded structure is usually adopted. According to the apparatus illustrated in the drawing of the foregoing prior art, repair of the piston packing requires removal of common lines (pipes) in the compressor. This is also a problem.
The apparatus for manufacturing a very large scale integrated circuit is usually operated 24 hours a day and for at least three weeks continuously. That is, a continuous operation of about 500 hours is usually performed. At every such three weeks, consumable portions are replaced as necessary. In a high-pressure operation of several hundred kgf/cm.sup.2, the durability of the piston packing in the compressor is about 500 hours. That is, at every 500 hours it is required to make replacement with new one. Besides, several hours are required until restoration to the original state after the replacement. Therefore, it is desirable that the replacement work be done in as simple a manner as possible and that removable of pipes which would cause generation of particles be avoided.
In these points the foregoing conventional compressor involves a problem in its utilization in the field of manufacturing very large scale integrated circuits such as silicon wafers.
It is an object of the present invention to provide a piston type gas compressor which dispenses with removal of pipe connections to simplify the replacement work of replacing a piston seal portion in such a conventional piston type gas compressor as referred to above and decrease the amount of metallic particles generated unavoidably in such replacement work.